Conventionally, in a stratified scavenging two-cycle engine having a scavenging flow passage, a method is frequently adopted in order to assuredly conduct stratified scavenging, in which a crank chamber and a cylinder chamber are connected via a hooked scavenging flow passage, which is composed of a vertical scavenging flow passage segment, provided outside the cylinder chamber, and a horizontal scavenging flow passage segment, for connecting the vertical scavenging flow passage segment and the cylinder chamber. The scavenging flow passage is often manufactured by gravity casting. However, the gravity casting method has a disadvantage in that the cost is high; therefore, manufacturing by die-casting is desirable. Examples of solutions to the above disadvantage are proposals made in Japanese Patent Publication (B2) No. 6-96185 and Japanese Utility Model Publication (Y2) No. 1-18813.
According to the disclosure in Japanese Patent Publication (B2) No. 6-96185, a cylinder liner is set within a cylinder block forming space, the inside of which is formed by using a plurality of die-casting dies. A die-casting die, for forming a scavenging passage horizontal segment which would penetrate to the outside of the cylinder block, and a die-casting die, for forming a scavenging passage vertical segment, extend within the cylinder block forming space, and molten metal is poured into the cylinder block forming space. After the molten metal is solidified, the die-casting dies are removed, and a blank cap is inserted into the outer portion of the scavenging passage horizontal segment which penetrates to the outside of the cylinder block, to block the opening to the outside of the cylinder block and thereby form an internal scavenging passage.
According to the aforesaid configuration, the cylinder liner is used for the cylinder block which is formed by the plurality of die-casting dies. In addition, in order to form a scavenging passage extending into the cylinder chamber, a protruding portion is formed on a die-casting die in such a manner as to form the scavenging passage horizontal segment which penetrates to the outside of the cylinder block. After casting, the die-casting die protruding portion is pulled out, and a blank cap is inserted into the outer portion of the formed scavenging passage horizontal segment, to thereby form the internal scavenging passage. Thus, the number of parts used, such as the cylinder liner, the die-casting die protruding portion, the blank cap, and the like, increases. Moreover, with the die-casting die protruding portion, the dies become more complicated and large-sized, and the cylinder block manufacturing processes and the working hours are increased. As a result, there arises a disadvantage in that the cost of manufacturing the cylinder block is high.
According to an art disclosed in Japanese Utility Model Publication No. 1-18813, an adapter, which includes a suction passage and a wall surface for forming a scavenging passage, is formed separately from the cylinder block; and the adapter is attached to an adapter attaching face, formed in the cylinder block, in order to form the scavenging passage.
However, in the latter configuration the adapter, which is separately formed, is attached to the adapter attaching face, which is formed on an outer peripheral face of the cylinder block, to form the scavenging passage, thereby increasing the number of parts, and complicating and increasing the manufacturing processes. Consequently, there arise disadvantages in that it takes more time to manufacture the cylinder block and the manufacturing cost becomes higher.